This is a nationalization of PCT/JP01/01156 filed Feb. 19, 2001 and published in Japanese.
The present invention relates to a printer for printing characters and the like indicating a route or location.
Conventionally, for example, a printer shown in FIG. 16 is known. The printer shown in FIG. 16 includes a sprocket 1, a platen roller 2, a thermal head 3, a sheet roll 4 on which a sheet is wound. The thermal head 3 is arranged on a cover 5. A ribbon cassette (not depicted) is mounted on this cover 5. Moreover, the cover 5 is mounted on a printer main body 7 in such a manner that the cover 5 can swing around a shaft 6.
The sprocket 1 and the platen roller 2 are arranged in the printer main body 7. A reference symbol 8 denotes a cutter for cutting the sheet. The cutter 8 is arranged in the printer main body 7. A drive gear mechanism for rotating the sprocket 1 and the platen roller 2 is also arranged in the printer main body 7.
In this printer, since the sprocket 1 is arranged downstream of the platen roller 2, a distance W between the thermal head 3 and the cutter 8 is significantly large. This results in a long blank space between the leading edge of the sheet to the position where a character is printed.
This blank space can be reduced by arranging the platen roller 2 downstream of the sprocket 1. However, in this case, to eliminate loosening of the sheet between the platen roller 2 and the sprocket 1, the platen roller 2 should have a circumferential speed slightly larger than the circumferential speed of the sprocket 1 when feeding the sheet.
However, upon printing start, the sprocket 1 starts rotation earlier than the platen roller 2 because of backlash and the sheet is loosened between the platen roller 2 and the sprocket 1. Thus, when the platen roller 2 has a fast circumferential speed, the feed-direction length is undesirably increased. That is, the printing distance accuracy becomes unstable.
It is therefore an object of the present invention to provide a printer comprising a printer main body, a cover arranged on the printer main body in such a manner that the cover can be opened, a sprocket for feeding a sheet from a sheet roll arranged in the printer main body, a platen roller for printing on the sheet, a printing head for printing on the sheet, a driving gear mechanism for rotating the sprocket and the platen roller, and a gear mechanism for rotating a ribbon core of an ink ribbon cassette mounted on the cover using the driving gear mechanism, wherein the sprocket and the platen roller are arranged in the printer main body, the printing head is arranged on the cover, and the platen roller is arranged downstream of the sprocket with respect to the forward conveying direction of the sheet, and wherein backlash eliminating means is further provided for eliminating backlash of the platen gear when the cover is closed.
According to the present invention, the platen roller is arranged downstream of the sprocket. This enables elimination of backlash of the platen gear when the cover is closed and reduces the blank space.